1. Field of the Invention
The present invention relates to apparatus and methods for manufacturing of thin-film photovoltaic modules in vacuum using physical vapor deposition.
2. Related Art
Photovoltaic (PV) modules convert solar energy into electricity through the photovoltaic effect. As such, photovoltaic modules represent a clean source of renewable energy in a global marketplace dominated by traditional fossil-fuel technologies, such as coal-fired and oil-fired power plants. However, to be a major source of energy within the global marketplace, PV modules must be manufactured as a commodity in quantities and at costs that are competitive with existing fossil fuel technologies.
One such PV module that satisfies the requirement of commodity manufacturing is a cadmium telluride (CdTe) PV module. CdTe PV modules generally take the form of thin film polycrystalline devices in which CdTe layer is paired with a cadmium sulfide (CdS) layer to form a hetero-junction. Although a variety of vacuum and non-vacuum processes can produce the thin films for a CdTe/CdS PV module, physical vapor deposition techniques, especially vacuum sublimation deposition of CdTe and CdS thin films, are especially amenable to the commodity manufacturing of CdTe/CdS PV modules. For example, vacuum sublimation of CdS and CdTe thin films can result in thin-film deposition rates ten to one hundred times higher than other suitable deposition techniques. Further, vacuum sublimation of the semiconductor layers in CdS/CdTe PV modules can be performed in modest levels of vacuum, thereby eliminating costly high-vacuum equipment common to existing deposition techniques.